1. Field of the Invention
The present invention relates to a zoom lens system and an image pickup apparatus using the same.
2. Description of the Related Art
In recent years, replacing a film camera, a digital camera in which, an object is photographed by using an image pickup device such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor) has become mainstream. Furthermore, in the field of digital cameras, there are several categories of digital cameras in a wide range from a high-function type for professional use to a compact popular type.
A user of a digital camera of a type belonging to the popular compact type seeks to enjoy photography by capturing readily various scenes at any time and anywhere.
Therefore, a small-size product, or a digital camera of a slim type which can be accommodated easily in a pocket of clothes or a bag, and carried conveniently has been preferred. Consequently, further small-sizing of a photographic lens system as well has been sought.
Whereas, there is a tendency towards an increase in the number of pixels of an image pickup element. Therefore, a high optical performance which deals with a large number of pixels of the image pickup element has been sought. Furthermore, for securing a mass productivity, it is necessary to suppress a sensitivity of degrading of the optical performance corresponding to a manufacturing error in a processing of lenses and an assembling process.
Moreover, from a point of view of widening a photography area, a zoom lens of a class with a zooming ratio of five times or seven times is becoming common, and further increase in the zooming ratio has been expected. Meanwhile, widening of an angle of field has also been expected. Zoom lens systems of various types have been proposed in response to such demands.
As a zoom lens system having a comparatively wide angle of field and high zooming ratio, and which is compact, a zoom lens system of a type which includes in order from an object side, a first lens unit having a negative refracting power, a second lens unit having a positive refracting power, a third lens unit having a negative refracting power, and a fourth lens unit having a positive refracting power has been known. For example, a zoom lens system of this type having a zooming ratio of about five times has been disclosed in Japanese Patent Application Laid-open Publication Nos. 2006-208889 and 2008-180901. Moreover, a zoom lens system having a zooming ratio of about 2.8 to 3 has been disclosed in Japanese Patent Application Laid-open Publication Nos. 2001-343587 and 2004-117828.